Leukoreducted blood products may be important in preventing transmission of cytomegalovirus and alloimmunization to human leukocyte antigens through blood transfusions. An efficient, highly sensitive, reliable method for detecting leukocytes particularly when present in low numbers (<5 x 10-6) is needed to streamline quality control of products considered "leukoreduced." Presently, a labor-intense, "gold standard" method that uses propidium iodide (PI) staining of leukocytes is performed to quantify small numbers of leukocytes. We are investigating the sensitivity and range of reliability of the newly available Imagen system to do the same by comparing it with PI staining.